A printed circuit board (PCB) is found in almost every electronic device. Besides keeping the components in place a PCB also provides electrical connections between the components mounted on it. As electronic devices have become more complex, and require more components, PCBs have become more densely populated with wiring and components.
A printed circuit board is typically formed as a flat plate or base of insulating material containing a pattern of conducting material. It becomes an electrical circuit when components are attached and soldered to it. The conducting material is commonly copper which has been coated with solder or plated with tin or tin-lead alloy. The usual insulating material is epoxy laminate; however there are many other kinds of materials that can be used as insulators. Single-sided boards are most common in mass-produced consumer electronic products. These single sided boards have all conductors on one side of the board. With two-sided boards, the conductors, or copper traces, can travel from one side of the board to the other through plated-thru holes called vias, or feed-throughs. In multilayer boards, the vias can connect to internal layers as well as the two outer layers.
The substrate of the board itself is an insulating and (usually, but not always) non-flexible material. Thin wires visible on the surface of the board are part of a copper foil that initially covers the entire board during the manufacturing process. In the manufacturing process this copper foil is partly etched away, and the remaining copper forms a network of thin wires. These wires are referred to as the “conductor pattern” and provide the electrical connections between the components mounted on the PCB.
Components that are mounted on one side on the board while its legs are soldered on the opposite side are called “Through Hole” components (THT: Through Hole Technology). Such components take up a large amount of space and require one hole to be drilled in the PCB for every leg. Hence, their legs occupy space on both sides of the board, and the connection points for them are also fairly large. On the other hand, THT components provide a better mechanical connection to the PCB compared to surface mounted devices, which will be discussed below. Connectors for cables and similar devices also have to withstand mechanical stress and are usually mounted using THT.
The legs of components that are made using “Surface Mounted Technology” (SMT) are soldered to the conductor pattern on the same side of the PCB as the component is mounted. This technology therefore does not require a hole in the PCB for every leg of the component. Surface Mounted Components (SMC) can be mounted on both sides of the PCB directly opposite each other.
To connect a PCB to another PCB an “edge connector” is often used. An edge connector may comprise small, uncovered pads of copper located along one side of the PCB. These copper pads are actually part of the conductor pattern on the PCB. The edge connector on one PCB is inserted into a matching connector (known as a “slot”) on the other PCB. In a PC, graphic boards, sound boards and other similar products are connected to the motherboard bus using edge connectors. The motherboard may be provided with different types of slots for devices conforming to different industry standards.
Besides cost, other important factors involved in PCB design are system compatibility and ease of use for the end user. System compatibility requires the board to interface both physically and electrically with the system where it is installed. For example, PCB boards conforming to the peripheral component interface (PCI) standard require the PCB board to have an edge connector that can interface with a corresponding slot both physically and electrically. The PCB may also have a bracket or equivalent means to facilitate installation in the computer housing. A PCB board manufacturer follows certain design criteria for a PCI interface to ensure compatibility with PCI-based systems. Layout of components and connectors should facilitate easy integration with the system and other compatible devices. With routing issues and limited space on a PCB, laying out components and connectors to enable a user friendly board design is often challenging.
These challenges are particularly significant in the context of laying out connectors for a redundant array of independent disks (RAID) controller board. RAID arrays comprise several disks that are grouped together in various organizations to improve performance and/or reliability of a computer's storage system. These disks are grouped and organized by a RAID controller. One typical form factor for a RAID controller is a PCB board, such as a PCI board, on which a control circuit is mounted. The control circuit exchanges signals with storage devices through connectors provided on the RAID controller board and thereby controls the operation of the storage devices. A typical RAID controller can manage around eight to twelve disk drives and hence requires eight to twelve connectors on the board. Since the connectors on a RAID controller board mate with corresponding disk drive connectors and cables, there may be eight to twelve drive connections per board. Some conventional designs place connectors in a random arrangement on the surface of the RAID controller board. The placement and orientation of such connectors often makes it cumbersome to mate disk drive connectors to the RAID board. Conventional connector layout often requires bending and routing of connector cables and prevents an orderly arrangement of connector cables.
The inventor has determined that there is a need for an improved approach to PCB board design that facilitates connection of cables between PCBs and devices connected to the PCBs. In particular, the inventor has found that there is a need for improved connector and cable routing arrangements in the field of RAID controller boards.